RARE PLANT SPECIES IN MASSACHUSETTS KATIIARINI; G. FIELD1 AND JONATHAN CODPINGTON 242 vascular plant species were listed as rare tn Massachusetts (Coddington & Field, 1978). There are several problems inherent in a state list of rare plants. Because the boundaries of states are politi- cal rather than natural, the plant species in a state represent diverse communities and ecosystems, some of which may be better repres- ented elsewhere. The historical occurrences of species in states are usually established from herbarium records, some of which may be inaccurate and need evaluation by experts. The publication of a 1 state rare plants list usually causes new information to come to light, rapidly making the list obsolete. I In Massachusetts, all of these problems obtain. Nevertheless, cer- I tain patterns of rarity can be distinguished among Massachusetts rare plant species, and these patterns arc broad enough to indicate general patterns in the distribution of rare plant species in the state. The 242 species on the Massachusetts rare plants list can be divided into groups: I) species rare throughout their ranges; 2) range limits: species at the northern or southern limits of their ranges: .1) species with highly disjunct distributions; and 4) species with a res- tricted total range; endemic to Massachusetts, endemic to New Eng- land, or endemic to a small geographic area. With the exception of a few species made rare by human activity alone (e.g. Rhododendron maximum (Ericaceae), collected by gardeners; Rihex americcma (Saxifragaeeae), the object of a government control program because it is the alternate host of a plant disease), most of the species on the Massachusetts rare plants list fit into these categories. SPKCIES RAItn THROUGHOUT TliriK WANG IS This category is typified by the orchid Isoiria mcdvoloidcs. which occurs from Ontario (Stewart, 197%) to North Carolina and Mis- souri (Eernald, 1950) but is nowhere common. The only known occurrence of this species in Massachusetts is documented by a herbarium sheet dated IK'Jy. AYtaria gvnU'ulttta (Gramineac), another Massachusetts species rare throughout its range, is one of the rare prairie species studied by Kabinowit/ (1978). The species appears to be adapted for long- distance dispersal. 'Present address: Pent, of Biology, Univ. of Oregon, Rugcm:, Oregon 151 152 Rhodora [v»i s: RANGL LIMITS Range limit species arc at the extreme edges of their distributions due to a combination of factors, such as reduced availability of suitable physical habitat and increased competition (Grant & Anto- novics. 1978). Many species on the Massachusetts rare plants list arc at the northern limits of their distributions. A few of these arc found in western Massachusetts. One occurs in woods(Cimicifuga racemosa, Ranunculaceae) The others are found in open habitats such as roadsides (e.g. Aster prenanthoides. Compositae) and meadows (e.g. Carex Bushii, Cyperaceae). A larger number of species at the northern limits of their ranges are found in eastern Massachusetts. A few of these occur in shaded habitats such as woods (e.g. Tipulu- ria discolor, Orchidaceac). Most occupy open or relatively open habitats, commonly sandy or peaty pond shores (e.g. Rfiyncfioxpora imtiuiata, Cyperaceae), sandy dry barrens (e.g. Onosmadium virgi- niamun, Boraginaccae), and other open habitats such as tidal mud flats, lake shores, fields, and roadsides. Some species at the northern limits of their distribution are found in both eastern and western Massachusetts. For these, the most common habitat is fresh-water pond shores (e.g. Fuirenapumila, Cyperaceae). Note that this habi- tat is found both in coastal areas and in western Massachusetts on sandy plains on the site of glacial Lake Hitchcock. A few species reach the southern limit of their ranges in Massa- chusetts. Five of these species occur in shaded habitats such as woods (e.g. Polysticliuni Braimii, Polypodiaccae). The others occur in habitats which are mostly open, such as bogs (e.g. Plata/it/tera obtii.tata, Orchidaceac) and open mountain tops (e.g. I.uzuki parvi- jlnra. .luncaceae). In eastern Massachusetts the species at the southern limits of their ranges are found in mostly open habitats such as pond shores (e.g. Isoeies faveoiata, lsoetaccae), sea beaches [fllymus arenaritts. Gra- mtneue), ledges and rocky beaches (e.g. Sagina nodosa, Caryophyl- laceae), and salt Hats (e.g. Stiaeda americana. Chcnopodiaceac). DISJtINC'IS In Massachusetts there are many disjunct localities of species that occur mainly to the south of the state. Only a few of these arc found in shaded habitats such as woods (e.g. Carcx Willdenowii, Cypera- ceae) and swamps {Magnolia virginiana. Magnoliaceae). Most of iyxo| Field & Coddington Massachusetts 153 the others occur in open habitats such as fresh water pond shores (e.g. Psihcarya nitens, Cyperaccae, and Eihitwdorw leneltus, Zos- teraceae), and barrens. A few disjunct localities of species occurring mostly to the north of the state are found in Massachusetts, occurring in such habitats as woods (e.g. ttalenia ilcjlexa, (Genttanaceac), sea beaches (e.g. Rumcxpalliilus, Polygonaccae), and "boreal" habitats such as mountain lops (e.g. Lycoodium St'luga, Lycopodiaceae), Some disjunct species in Massachusetts cannot be characterized as northern or southern species. Some are widespread species infrc- % qucntly distributed throughout their ranges. Others are restricted in |jt total distribution. Several Massachusetts disjunct species occur in Nova Scotia, Cape Cod and Massachusetts offshore islands. Block Island, Rhode Island, Long Island, New York, and New Jersey, sometimes extending farther south along the coastal plain. Exam- ples of this include Sahatia Kertnedyana (Genttanaceac), which j occurs in Nova Scotia, eastern Massachusetts and Rhode Island, f southeastern North Carolina and northeastern South Carolina (Perry, 1971); and Corema CoMfW/f (Empetiaceae), found in nor- theastern Canada including Nova Scotia, sporadically south on the i coast to outer Cape Cod, and in the New Jersey Pine Darrens (I er- nald. 1950). [;NIM;MICS AND RI:STRUTI;I)-RAN(;I; sri;nj:s There arc taxonomie questions about many of the tax a listed as Massachusetts or New England endemics and restricted species. Sometimes named as species and sometimes as varieties, these tax a may represent hybrids, geographically isolated populations, cco- types, newly-evolved or relict species. With the exception of Parony- chiti argyroiomtt var. alhi-montana (Caryophyllaccac), all of them are associated with the coastal plain, and most occupy open habitats. Only two plant taxa have ever been considered to he endemic to Massachusetts. One, Jancus pervettis. was only known from one locality on Cape Cod, where it apparently persisted for a few years. The habitat a I this site has been severely altered, but even before habitat changes occurred, the plant could no longer be found. Unless it can be relocated, its status as a species will remain in question. 154 Rhodora [v(»t. x: The other Massachusetts endemic is Amclanchier nantucketemis (Rosaceae), a Nantucket shrub. This was originally distinguished from other Amelanchier species because of" its smaller size, spread- ing habit, and short petals (Bicknetl, 1911). Later studies of the genus (Wcigand, 1912; Jones, 1946) considered A. nantucketemis to be part of such other species as A. oblongifoUa var. tnicropeiata and A. canadensis. According to both Wcigand (1912) and Fernald (1946, 1950), the genus Amelanchier frequently forms hybrids. Field observations by Coddington (1978, unpublished) suggest that wha- tever the origin and species status of A. nantucketemis, it is a recog- nizable entity in the field. It occurs on shores of fresh water ponds and in sandy barrens. Three taxa on the Massachusetts rare plants list are endemic to New England: fsoetes foveoiata (Isoetaceae), Paronychia argyro- coma var. albimontana (Caryophyllaccae), and Eupatorium leu- colepis var. novai'-angtiae(Compositac). The genus fsttetes is poorly understood and poorly collected (R J. Mickey, pers. comm.); until more work is done on it, the status of I. foveoiata, a shallow-water aquatic found in southern New Hampshire and Massachusetts, remains questionable Paronychia argyrocoma var. albi-tnontana is a highly disjunct variety of a species which otherwise occurs in Virginia, West Virginia, North Carolina, Georgia, and Tennessee (Core, 1941). Variety albi-tnontana is found at a few localities on rocky mountains in southern Maine and New Hampshire, and on a rocky island at sea level in northeastern Massachusetts, Eupatorium feucolepis var. novae-angliae. another disjunct variety, is limited to southeastern Massachusetts and Rhode Island, where it occurs in sandy soil near fresh water ponds. Twelve species on the Massachusetts rare plants list have a res- tricted distribution. Two are western disjuncts {l.mhvigiapolycarpa, Onagraceac, and Psihcarya nitens, Cyperaceac), occurring in ex- tremely limited areas on the eastern coastal plain and also in the midwest. Other species (e.g. two tsoetes species, two liidens species) are poorly defined and understood taxonomically. Sahatia Kettne- dyana ((icntianaccae), a notable disjunct mentioned above, occurs in Nova Scotia, coastal Massachusetts and Rhode Island, and the Carolinas. Two species of dry sandy areas, ffetianthenium Junto- sum (Cislaccac), and Agatinis at lira (Serophulatiaceae), occur only in eastern Massachusetts, Rhode Island, Connecticut, and Long Island. Populations of //. dumosum were relocated